Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $186.40   3.233%   $192.4263   $192.43   $192.45   $192.40  
  Purchase #2 $199.37   4.794%   $208.9278   $208.93   $208.95   $208.90  
  Purchase #3 $137.62   13.857%   $156.69   $156.69   $156.70   $156.70  
  Purchase #4 $161.75   9.756%   $177.5303   $177.53   $177.55   $177.50  
  Purchase #5 $195.88   13.188%   $221.7127   $221.71   $221.70   $221.70  
  Purchase #6 $159.76   12.461%   $179.6677   $179.67   $179.65   $179.70  
  Purchase #7 $148.82   6.623%   $158.6763   $158.68   $158.70   $158.70  
  7 purchase totals = $1,189.60       $1,295.6311   $1,295.64   $1,295.70   $1,295.60